I think that's a bit of an exaggeration. My old company (Acquia) kept a lot of customers up through the various outages with mere two-zone redundancy. You do n

I think that's a bit of an exaggeration. My old company (Acquia) kept a lot of customers up through the various outages with mere two-zone redundancy. You do need to actually engineer for failover and recovery, though. That point is correct: It doesn't necessarily help you to have half of your servers survive an outage if that still kills your service or requires painful amounts of manual intervention. And it really is a lot easier to just shrug, keep your backups up to date, and pray for your zone to come back ASAP. Do your cost-benefit analysis.